1. Field of the Invention
The present invention relates to a double swing power unit for use in a plasma nuclear fusion experimental system.
2. Description of the Prior Art
FIG. 1 is a circuit diagram showing a prior art double swing power supply circuit described in a paper entitled "Current Transformer Coil Power Source for Generating Reversed Magnetic Field Pinched Plasma by Double-Swing Magnetic Flux", the Transactions of the Institute of Electrical Engineers of Japan, Vol. B106, No. 3, pp. 241-248, March 1986. The circuit as shown in FIG. 1 is, in the field of plasma nuclear fusion, in use for a power source on the primary side in transformer coupling with the plasma current for such confinement devices as a tokamak achieving the confinement by passing a plasma current through torus plasma in the torus direction and a reverse magnetic field pinch (hereinafter to be called RFP), for a toroidal coil power source in the RFP, and the like.
Referring to FIG. 1, reference numeral 100 denotes a load coil, 101 denotes a decoupling inductor, 102 denotes a bias capacitor bank, 103 denotes a reverse capacitor bank, 104 denotes a hold capacitor bank, 105 denotes a bias switch, 106 denotes a reverse switch, 107 denotes a hold switch, and 108 denotes a crowbar switch. Incidentally, + and - signs given to each capacitor bank indicate the charged polarity before discharging. The load coil current in the electric circuit is shown in FIG. 2.
Operation will be described with reference to FIG. 1 and FIG. 2. At the start, the capacitors are charged as shown by the signs. Then, first, at the time point t.sub.0, the bias switch 105 is closed so that a current is passed through a load coil 100 via the decoupling inductor 101. Then, at the time point t.sub.1, the reverse switch 106 is closed and thereby a current from the reverse capacitor bank 103 is started to flow through the load coil 100 in the reverse direction. The decoupling inductor 101 is used so that no large current may flow into the bias capacitor bank 102 at this time. As a result, the load coil current is greatly reduced. Then, at the time point t.sub.2, the hold switch 107 is closed.
At this time, if the charged voltages on the hold capacitor bank 104 and the reverse capacitor bank 103 are equal, no current flows there between. And, the current flowing through the load coil 100 is maintained or increased. Finally, at the time point t.sub.4, the crow bar switch 108 is closed and the load coil current flows back.
Since prior art double swing power unit was structured as described above, there have been problems such that the current flowing through the load coil is affected by the currents flowing between each of the capacitor banks and that, in order to change the load coil current at a desired time point, an additional capacitor bank must be provided separately.